A college professor from St. Louis, Missouri has released research claiming that the U.S. Army conducted secret Cold War tests by spraying toxic radioactive chemicals on cities like St. Louis and Corpus Christi.

St. Louis Community College-Meramec sociology professor Lisa Martino-Taylor told The Associated Press that her research showed that the Army may have sprayed radioactive particles with zinc cadmium sulfide while claiming that it was testing a smoke screen that could prevent Russians from observing St. Louis from the air.

Those tests were concentrated in predominately-black areas of the city, which Army documents called “a densely populated slum district.”

In 1994, the Army confirmed to Congress that St. Louis was chosen because it resembled Russian cities that the U.S. might have to attack with biological weapons.